New fluorescent polymer makes deformation visible

18 August 2015

Dutch chemists have developed a novel kind of polymer than can report when it changes shape: after exposure to UV light, the polymer molecules emit a different color of light. This opens a new pathway for research into how viruses function in a cell and how minor damage in rubber and plastics can accumulate and lead to rupture. The new polymers were developed by researchers at Wageningen University in the Netherlands, who have published a paper on their research in the Journal of the American Chemical Society.

Polymers can be as straight as uncooked spaghetti, but they can also occur as a tangle of cooked spaghetti. Polymer chains resist changes to their conformation, such as when they are stretched. This spring-like effect confers elasticity on rubber, flexibility on plastics and strength on the cytoskeleton of the cell. To change the conformation of a polymer, force must be applied to the molecule, but figuring out the exact conformation of a polymer is particularly difficult, especially if the polymers are surrounded by many other substances, such as in a cell.

A team of researchers from the Physical Chemistry and Soft Matter Group of Wageningen University, led by Joris Sprakel, has now designed a new kind of polymer that 'reports' its spatial configuration through the light it emits. PhD candidate Hande Cingil carried out the work on the water-soluble semiconducting polymers, which the researchers have named conjugated polyelectrolytes (CPEs).

Luminescent polymers, which change color as their conformation changes, have existed for some time. A special feature of the CPE polymers is that nuances can be observed in these color changes. Following irradiation with UV light, the CPE polymers emit a color spectrum that looks like the profile of a mountain with a flat top. But as their conformation changes, such as due to stretching, characteristic peaks begin to appear in the spectrum, even when the polymers are only exposed to very small forces at the nanoscale.

In their paper, the Wageningen chemists demonstrate the functioning of the CPE polymers. For this purpose, they used a protein that was designed by their colleagues in Wageningen, Renko de Vries and Martien Cohen Stuart. This protein is a highly simplified version of an artificial virus; like a biological virus, it binds to DNA and subsequently encapsulates it, but it will also encapsulate the CPE polymer.

“In our experiment, the CPE was encapsulated by the simplified artificial virus protein, giving it a rigid layer, which caused the polymer to change shape,’ explains Sprakel. “Using simple and non-invasive light spectroscopy, this encapsulation process can now be studied in detail.”

The CPE polymer can be used for many purposes. For example, groups of molecules can be attached to the polymer for specific applications, such as the detection of proteins or toxins. It also offers an improved method for determining exactly how viral proteins stretch and fold to encapsulate DNA, or how very minor damage to polymeric materials gradually accumulates and eventually causes the materials to rupture.

The researchers are even working on extending this research beyond showing whether a polymer chain has stretched: they aim to show exactly where in the chain this stretching occurs.

This story is adapted from material from Wageningen University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

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